An approach toward the synthesis of euonyminol and cathedulin K- 19 PublicDeposited

Descriptions

A synthetic approach toward the two major fragments of cathedulin K-19,
euonyminol (4) and dimethyl cathate (69), was investigated. Synthesis of
dimethyl cathate was accomplished in 3 steps starting from 73. Efforts directed
towards the synthesis of euonyminol, a highly oxygenated dihydroagarofuran
sesquiterpene, was advanced to a stage in which most of the A ring of 4 was
completed. Compound 79 was used as a starting material which was obtained
from a Diels-Alder reaction of 80 and 81. Subsequent bromination of 79 and
elimination of hydrogen bromide afforded 93 in a one-pot operation. A
remarkable chemo- and stereoselective reduction of 93 under Luche conditions
gave 94 and the latter was epoxidized stereoselectively by m-chloroperbenzoic
acid to yield 91. Introduction of an isopropenyl moiety to 91 was accomplished
following Liotta's protocol to provide 145. Vanadium catalyzed epoxidation
installed the epoxide moiety of 152a with good stereoselectivity. Two
approaches towards 4 from the key intermediate 152a were pursued. The first
approach entailed the epoxide cascade reaction of 152a. Treatment of 152a
with trifluoro- or trichloroacetic acid afforded 165 and 166, respectively, which
possessed most of the functionality required for 4. The second route to 178
proceeded in 5 steps from 152a. Treatment of 152a with titanium
tetraisopropoxide afforded 168, which was cyclized to 169 under acid catalysis.
The diol moiety of 169 was protected as a benzylidene acetal and subsequent
hydroxylation following Davis' procedure afforded 171. Stereoselective
reduction of 171 using lithium aluminum hydride in the presence of titanium
tetraisopropoxide provided 178.